CONCEPT
Marr's Three Levels of Analysis
The framework that any information-processing system—brain or machine—must be understood at three distinct levels: the computational (what problem is solved and why), the algorithmic (by what procedure), and the implementational (in what physical stuff), and that confusing them is the source of most bad theorizing about minds.
When
David Marr set out to understand vision, he realized his field had not agreed on what kind of question it was asking. His response was a framework—perhaps the most disciplined one ever proposed for the science of mind—that separates three genuinely distinct levels of analysis. The computational level asks what problem a system solves and why that is the right problem: it is the level of the abstract task, of function, of the logic by which the correct output follows from the input. The algorithmic level asks how: what representation the system uses for inputs and outputs, and what procedure transforms one into the other. The implementational level asks in what physical stuff: neurons, transistors, gears. Marr’s central, unfashionable claim was that these levels are genuinely separate—answers at one do not substitute for answers at another—and that their dependence runs top-down: the computational constrains the